The present invention relates to a storage control unit for controlling storage devices, such as magnetic disk devices, magnetic tape devices, optical disk devices, opt-magnetic disk devices, library devices and so on, so as to manage input/output (accesses) thereof to a host apparatus or device(s) of higher level, and in particular to a controller and a data storage system using thereof, in which fiber channels are used as routes or channels for accessing to such the storage devices.
In more detail, the present invention relates to a computer system, in which fiber channels standardized by ANSI X3T11 are applied as interfaces among the host computer(s), the storage devices such as the magnetic disk devices, and the storage control unit(s), and relates to a data storage system, in which a new storage control unit(s) is added to during an online operation of the computer system, thereby enabling to disperse or decentralize loads between or among the storage control units or to centralize functions which are conducted by plural controllers.
Conventionally, relating to install of an additional storage control unit(s), for example in Japanese Patent Laying-Open No. Hei 7-20994 (1995), there is described an enlargement in scale, especially, in a memory system of a large-scaled computer, by means of additional installations of a connecting adopter to the host computer in the memory system, a connecting adopter to the disk drive device and a shared cache memory, as well as function of inserting and extracting of live wires. And, there is proposed a manner wherein, the connecting adopter to the host computer, the connecting adopter to the disk drive unit and the shared cache memory mentioned above are installed one by one on an interior bus in the memory system.
The technology disclosed in Japanese Patent Laying-Open No. Hei 7-20994 (1995) adopts a shared cache memory method which is used generally in the memory system of the large-scaled computer, wherein each of the adopters connecting to the host computer(s) reads control information in a logical unit(s) located in the shared cache memory on the interior bus, sequentially, therefore it is able to access to a random logical unit without necessity of process of succession (i.e., taking over) or transfer of the control information of the logical unit between the connecting adopters to the host computer(s).
Also, relating multiplexing of the storage control units, each having the cache memory, for example in Japanese Patent Laying-Open No. Hei 7-160432 (1995), there is described a method, wherein the storage control unit is duplicated, while one of the storage control units is in a waiting condition as a standby storage control unit when occurring trouble in the other, thereby achieving redundancy of the storage control unit. Further, in Japanese Patent Laying-Open No. Hei 8-335144 (1996), there are also described the decentralization of loads by duplication of the storage control units and the redundancy of thereof when occurring problem therein.